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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

5809 results found.

  1. SVOM GRB 260504B: MASTER-OAFA optical observations
  2. Fermi GRB 260504A: Global MASTER-Net observations report
  3. GRB 260504A: Fermi GBM Final Real-time Localization
  4. EP260502a: BOOTES-7 observations of a fading catalogued source close to the X-ray position
  5. Fermi GRB 260429A: Global MASTER-Net observations report
  6. EP260430a: Global MASTER-Net observations report
  7. Fermi GRB 260428A: Global MASTER-Net observations report
  8. EP260416a: Mondy and Terskol optical upper limits
  9. Fermi trigger No 798737427: Global MASTER-Net observations report
  10. Fermi GRB 260421C: Global MASTER-Net observations report
  11. Fermi GRB 260421B: Global MASTER-Net observations report
  12. Fermi GRB 260421A: Global MASTER-Net observations report
  13. GRB 260419A: Fermi GBM Final Real-time Localization
  14. Fermi GRB 260417B: Global MASTER-Net observations report
  15. EP260416a: Ondrejov D50 optical detection
  16. EP260417a: Global MASTER-Net observations report
  17. Fermi GRB 260417A: Global MASTER-Net observations report
  18. EP260416a: LCO observations confirm end of flaring phase
  19. Fermi trigger No 797912738: Global MASTER-Net observations report
  20. The EP-WXT trigger 01709260122 is likely a flaring star
  21. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  22. EP260409a: SVOM/VT optical upper limits
  23. EP260409a: COLIBRÍ optical upper limits
  24. GRB 260407A: CALET Gamma-Ray Burst Monitor detection
  25. EP260409a: Global MASTER-Net observations report
  26. GRB 260407A: Glowbug gamma-ray detection
  27. GRB 260407A: Fermi GBM Final Real-time Localization
  28. EP260405a: Global MASTER-Net observations report
  29. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  30. Fermi trigger No 797039833: Global MASTER-Net observations report
  31. EP260324A / AT 2026hir: COLIBRÍ optical observations
  32. GRB 260401A: MAXI/GSC detection
  33. EP260329b: J-band upper limits with WINTER
  34. EP260327a: Global MASTER-Net observations report
  35. IPN triangulation of GRB 260320A
  36. EP260321a: Upper limits from a neutrino search with IceCube
  37. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  38. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  39. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  40. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  41. EP260321a: Global MASTER-Net observations report
  42. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  43. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  44. GRB 260310A / AT2026fgk: LCO optical observations
  45. IceCube-260315A: COLIBRÍ optical observations
  46. EP260314a: optical upper limit with Kinder observations
  47. GRB 260310A / AT 2026fgk: iTelescope optical observations
  48. EP260314a: COLIBRÍ optical upper limit
  49. GRID detection of GRB 260312B
  50. EP260314a: Global MASTER-Net observations report
  51. Fermi trigger No 795185313: Global MASTER-Net observations report
  52. GRB 260310A / AT2026fgk: SAO RAS optical observations
  53. Fermi GRB 260313A: Global MASTER-Net observations report
  54. GRB 260312B: AstroSat CZTI detection
  55. GRB 260310A / AT2026fgk: CAHA 1.23m telescope optical observations
  56. GRB 260312B: Glowbug gamma-ray detection
  57. Fermi GRB 260311B: Global MASTER-Net observations report
  58. GRB 260312B: BALROG localization (Fermi Trigger 795001611 / GRB 260312407)
  59. GRB 260312B: Fermi GBM Final Real-time Localization
  60. EP260306a: Mondy optical upper limit
  61. Fermi GRB 260310B: Global MASTER-Net observations report
  62. GRB 260207A: TESS Detection and Possible VLA Counterpart
  63. GRB 260303A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  64. GRID detection of GRB 260223A
  65. GRB 260225A: WINTER J-band upper limit
  66. LAT GRB260226.44: Global MASTER-Net observations report
  67. Fermi GRB 260226A: Global MASTER-Net observations report
  68. GRB 260225A: SVOM/COLIBRÍ (FM-GFT) Detection of an Optical Counterpart Candidate
  69. GRB 260225A: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  70. EP260223a: Xinglong optical upper limit
  71. GRB 260223A: BALROG localization (Fermi Trigger 793512674 / GRB 260223174)
  72. Fermi GRB 260223A: Global MASTER-Net observations report
  73. GRB 260223A: Fermi GBM Final Real-time Localization
  74. GRB 260222A: Fermi GBM Final Real-time Localization
  75. EP260221a: Xinglong optical upper limit
  76. IceCube Alert 260217A: Global MASTER-Net observations report
  77. Fermi-LAT Gamma-ray Observations of IceCube-260217A
  78. GRB 260217A: Fermi GBM Final Localization
  79. GRB 260208A: continued Mondy optical observations
  80. GRB 260206A: probable hard X-ray burst from 4U 0513-40
  81. EP260214b: LCO optical counterpart detection
  82. EP260213a: COLIBRÍ optical upper limits
  83. GRB 260213B: BALROG localization (Fermi Trigger 792697214 / GRB 260213736)
  84. Fermi GRB 260212A: Global MASTER-Net observations report
  85. Fermi GRB 260210C: Global MASTER-Net observations report
  86. EP260210a: Global MASTER-Net observations report
  87. GRB 260208A: LCO detection of the optical counterpart
  88. GRB 260208B: AstroSat CZTI detection of a bright long burst
  89. GRB260208A: Liverpool Telescope optical follow-up observations
  90. Fermi GRB 260209A: Global MASTER-Net observations report
  91. GRB 260208A: Liverpool Telescope optical detection
  92. Fermi GRB 260208C: Global MASTER-Net observations report
  93. Fermi GRB 260208D: Global MASTER-Net observations report
  94. GRB 260208B: Fermi GBM Detection
  95. GRB 260208B: Fermi-LAT detection
  96. GRB 260208B: BALROG localization (Fermi Trigger 792237169 / GRB 260208412)
  97. GRB 260208B: Fermi GBM Final Real-time Localization
  98. GRB 260206A: Swift-XRT observations
  99. GRB 260206A (or XRB from 4U 0513-40): MAXI/GSC detection
  100. GRB 260204A: Swift-XRT observations

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